U.S. Patent Application No. 2005/0013474 discloses a device wherein the edge area of a wafer is also examined or inspected with the help of three cameras. However, the document does not discuss the design of the illumination means for the edge area of the wafer.
U.S. Patent Application No. 2003/0169916 discloses a device using three cameras to acquire images of the front side of the wafer edge and of the two chamfers at the wafer edge, respectively. The cameras are arranged such that the first camera is opposite to the upper chamfer of the wafer edge, that a second camera is opposite to the front side of the wafer edge, and that a third camera is opposite to the lower chamfer of the wafer edge. The patent application does not discuss the design of the illumination means for illuminating the wafer edge.
German Patent application DE 10 2007 024 525.6, which has not been laid open yet, discloses a device and a method for evaluating defects in the edge area of a wafer. In one embodiment, an illumination means is described that is designed as an annular segment. The illumination means is a calotte having a plurality of light sources attached thereto. The calotte is provided with a diffusely transparent screen or a diffuser, which thus contributes to a higher homogeneity of the illumination. The calotte comprises a recess via which the edge of the wafer is captured. The wafer extends into the interior of the calotte. The illumination elements arranged on the calotte may be implemented as LEDs emitting white light. Illumination elements are arranged on the calotte such that a bright field illumination is achieved at the edge of the wafer.